1. Field of the Invention
This invention relates to a lighting device and more particularly to a lighting device capable of emitting a light over a desk top surface with substantially uniform illuminance.
2. Description of the Prior Art
A conventional lighting device disclosed, for example, in the U.S. Pat. No. 4,054,793 has a light source and reflector set in a housing provided with an illumination opening. This type of lighting device is so constructed as to cause a light to be emitted over, for example, the top of an office desk. The illumination opening is provided with a transparent light-refracting plate whose inner wall is cut in the form of a series of prisms or in the knurled form. This light-refracting plate indeed prevents veiling reflection of a light. With the lighting device of the above-mentioned U.S. Pat. No. 4,054,793, however, a reflector disposed at the back of a light source is designed to reflect a light flux from the source only downwardly, causing the desk top surface to be irregularly illuminated. In other words, the proposed lighting device has a drawback in that the portion of the top surface of an office desk which lies near a lighting device is more brightly illuminated, whereas that portion of the desk top surface which lies remote from the lighting device receives a smaller amount of light; namely, that region of the desk top surface which lies immediately in front of the user working with such desk gets darker. If it is desired to eliminate the darkness in front of the user, then it will be necessary to provide a light source device capable of emitting a brighter light. This means that the resultant lighting device will consume more electric power, be increased in size and obstruct the user's front view.